1. Field of the Invention
The present invention relates to a method for manufacturing a display device using an n-channel thin film transistor and a p-channel thin film transistor.
2. Description of the Related Art
In recent years, a technology to form thin film transistors using semiconductor thin films (with a thickness of approximately several tens to several hundreds of nanometers) that are formed over substrates having an insulating surface has attracted attention. Thin film transistors have been widely applied to electronic devices such as ICs and electro-optical devices and rapidly developed especially as switching elements for image display devices.
A Thin film transistor using an amorphous silicon film for a channel formation region, a thin film transistor using a polycrystalline silicon film for a channel formation region, or the like are used as a switching element in an image display device. As a method for forming polycrystalline silicon films, a technology is known in which a pulsed excimer laser beam is processed into a linear shape by an optical system and an amorphous silicon film is scanned and irradiated with the linear beam for crystallization.
In addition, as switching elements of image display devices, thin film transistors using a microcrystalline silicon film as a channel formation region are used (Patent Document 1: Japanese Published Patent Application No. H4-242724, Non-Patent Document 1: Toshiaki Arai et al., SID 07 DIGEST, 2007, pp. 1370-1373).
In the meantime, a liquid crystal panel is manufactured in such a manner that a plurality of panels are processed over a glass substrate having large area, which is referred to as a mother glass, and then are finally cut to have sizes each of which fit a screen of a television or a personal computer. This is because the plurality of panels are formed from one piece of mother glass, so that cost per one panel is reduced. In the market of liquid crystal televisions, increase in screen size (panel size) and steep drop in retail price occurs. For these past several years, increase of mother glass size has proceeded in order to improve productivity in response to increase in screen size and price drop.
A size of a typical glass substrate around 1991 is 300 mm×400 mm, which is called the first generation. After that, a size of a mother glass has kept on increasing as follows: the second generation (400 mm×500 mm), the third generation (550 mm×650 mm), the fourth generation (730 mm×920 mm), the fifth generation (1000 mm×1200 mm), the sixth generation (2450 mm×1850 mm), the seventh generation (1870 mm×2200 mm), the eighth generation (2000 mm×2400 mm), the ninth generation (2450 mm×3050 mm), and the tenth generation (2850 mm×3050 mm).